Universal mobile telecommunications system (UMTS) is a 3rd generation (3G) asynchronous mobile communication system operating in wideband code division multiple access (WCDMA) based on European systems, global system for mobile communications (GSM) and general packet radio services (GPRS). The long-term evolution (LTE) of UMTS is under discussion by the 3rd generation partnership project (3GPP) that standardized UMTS.
In 3GPP LTE, a base station (BS) needs to know a type of data and an amount of data which each user wants to transmit for using uplink radio resources efficiently. For downlink radio resources, a BS can know an amount of data need to be transmitted to each user through downlink, since the data to be transmitted through the downlink is transferred from an access gateway to the BS. On the other hand, for uplink radio resources, if a user equipment (UE) does not inform a BS information on data to be transmitted through uplink, the BS cannot know how much uplink radio resources are required for each UE. Therefore, for a BS to allocate uplink radio resources to a UE properly, the UE is required to provide information for scheduling the uplink radio resources to the BS.
Accordingly, if there is data to be transmitted to a BS, a UE inform the BS that the UE has the data to be transmitted to the BS, and the BS allocates proper uplink radio resources to the UE based on the information. This procedure is called a buffer status reporting (BSR) procedure.
A UE needs uplink radio resources for transmitting a BSR to a BS. If the UE has allocated uplink radio resources when the BSR is triggered, the UE immediately transmits the BSR to the BS using the allocated uplink radio resources. If the UE does not have allocated uplink radio resources when the BSR is triggered, the UE performs a scheduling request (SR) procedure for receiving uplink radio resources from the BS.
Transmit power needs to be properly regulated in order for a user equipment (UE) to transmit data to a base station (BS). When the transmit power is too low, the BS may not be able to correctly receive the data. When the transmit power is too high, even though the UE can receive data without any problem, it may act as an interference to another UE for receiving data. Therefore, the BS needs to optimize power used in uplink transmission of the UE from a system aspect.
In order for the BS to regulate the transmit power of the UE, essential information must be acquired from the UE. For this, power headroom reporting (PHR) of the UE is used. A power headroom implies power that can be further used in addition to the transmit power currently used by the UE. That is, the power headroom indicates a difference between maximum possible transmit power that can be used by the UE and the currently used transmit power. Upon receiving the PHR from the UE, the BS can determine transmit power used for uplink transmission of the UE at a next time on the basis of the received PHR. The determined transmit power of the UE can be indicated by using a size of a resource block (RB) and a modulation and coding scheme (MCS), and can be used when an uplink (UL) grant is allocated to the UE at a next time. Since radio resources may be wasted if the UE frequently transmits the PHR, the UE can define a PHR trigger condition and transmit the PHR only when the condition is satisfied.
In order to allow users to access various networks and services ubiquitously, an increasing number of UEs are equipped with multiple radio transceivers. For example, a UE may be equipped with 3GPP LTE, Wi-Fi, and Bluetooth transceivers, and global navigation satellite system (GNSS) receivers. Due to extreme proximity of multiple radio transceivers within the same UE operating on adjacent frequencies or subharmonic frequencies, the interference power coming from a transmitter of the collocated radio may be much higher than the actual received power level of the desired signal for a receiver. This situation causes in-device coexistence (IDC) interference. The challenge lies in avoiding or minimizing IDC interference between those collocated radio transceivers, as current state-of-the-art filter technology might not provide sufficient rejection for certain scenarios.
When a UE experiences a level of IDC interference that cannot be solved by the UE itself and a network intervention is required, the UE transmits an DC indication via dedicated radio resource (RRC) signaling to report the problems. The details of the IDC indication trigger may be left up to UE implementation. It may rely on existing LTE measurements and/or UE internal coordination. The IDC indication should be triggered based on ongoing IDC interference on the serving or non-serving frequencies, instead of assumptions or predictions of potential interference. A UE that supports IDC functionality indicates this capability to the network, and the network can then configure by dedicated signaling whether the UE is allowed to transmit an IDC indication. The UE may only transmit an IDC indication for E-UTRA UL/DL carriers for which a measurement object is configured.
The term “ongoing IDC interference” should be treated as a general guideline by the UE. For the serving frequency, ongoing interference consists of interference caused by aggressor radio to victim radio during either active data exchange or upcoming data activity which is expected in up to a few hundred milliseconds. For the non-serving frequency, ongoing interference is an anticipation that the LTE radio will either become aggressor or victim if it is handed over to the non-serving frequency. Ongoing interference is applicable over several subframes/slots where not necessarily all the subframes/slots are affected.
When notified of IDC problems through an IDC indication from the UE, a BS can choose to apply a frequency division multiplexing (FDM) solution or a time division multiplexing (TDM) solution:                The basic concept of an FDM solution is to move the LTE signal away from an industrial, scientific and medical (ISM) band by performing inter-frequency handover within E-UTRAN.        The basic concept of a TDM solution is to ensure that transmission of a radio signal does not coincide with reception of another radio signal. LTE discontinuous reception (DRX) mechanism is considered as a baseline to provide TDM patterns (i.e. periods during which the LTE UE may be scheduled or is not scheduled) to resolve the IDC issues. DRX based TDM solution should be used in a predictable way, i.e. the BS should ensure a predictable pattern of unscheduled periods by means of DRX mechanism.        
To assist the BS in selecting an appropriate solution, all necessary/available assistance information for both FDM and TDM solutions is transmitted together in the IDC indication to the BS. The IDC assistance information contains the list of E-UTRA carriers suffering from ongoing interference and, depending on the scenario, it also contains TDM patterns or parameters to enable appropriate DRX configuration for TDM solutions on the serving E-UTRA carrier. The IDC indication is also used to update the IDC assistance information, including for the cases when the UE no longer suffers from IDC interference. A prohibit mechanism is used to restrict the interval at which the UE transmits the IDC indication. In case of inter-eNB handover, the DC assistance information is transferred from the source BS to the target BS.
From the start of IDC interference detection to the delivery of the corresponding IDC indication to the network, it is up to the UE whether radio resource management (RRM) measurements reflect IDC interference. After the successful transmission of the IDC indication though, the UE shall ensure that RRM measurements are free of IDC interference.
In addition, the UE can autonomously deny LTE transmission to protect ISM in rare cases if other solutions cannot be used. Conversely, it is assumed that the UE also autonomously denies ISM transmission in order to ensure connectivity with the eNB to perform necessary procedures to resolve IDC problems. The use of autonomous denials is not limited to handover scenarios. There could be a limit on the amount of denials known to both UE and eNB.
As describe above, if a UE has some data to transmit, the UE may transmit a BSR to a BS. Based on the information from the received BSR, the BS may allocate UL grants to the UE. Then, the UE can transmit the data by using the allocated UL grants.
However, if the UE needs to deny the UL grants to protect the ISM transmissions, the allocated UL grants will be just wasted because they cannot be used by the other UEs.
Therefore, it is important to minimize the impact of the autonomous denials that results in waste of the UL resources.